Subterranean storage of fluids



May 14, 1963 G. M. cLoss ETAL SUBTERRANEAN STORAGE OF FLUIDS 2Sheets-Sheet 1 Filed March 25, 1960 6 2 mv 2 v V m IM. 2 O V 92 V MUINVENTORS GEORGE M. GLOSS BYPATRICK F. DOUGHERTY May 14, 1963 G. M.cLoss ETAL SUBTERRANEAN STORAGE OF FLUIDS 2 Sheets-Sheet 2 Filed March25, 1960 s R m A m f V A m .l v .w .M/h. 2 v\ A GEORGE M. GLOSSmFKATRIOK F. DOUGHERTY @um s La TTORNEY United States Patent Oiitice3,089,309 Patented May 14, 1963 3,089,369 SUBTERRANEN STRAGE @E FLUIDSGeorge M. Class, Bryn Mawr, and Patrick F. Dougherty, Chester Heights,Pa., assignors to Sun @il Company, Philadelphia, Pa., a carpet-ation ofNew Iersey Fiieti Mar. 25, 196%, Ser. No. 17,662 2 Claims. (Cl. 61.)

This invention relates to the subterranean storage of uids underpressure, and more particularly to a mined rock cavern arrangement forthe storage of such uids.

Subterranean caverns of the aforesaid type, which may be mined in rock(granite) for example, are constructed by employing for excavation alarge-diameter verticallyextending main or working shaft, through whichmen, materials, and equipment may be lowered to the cavern itself, andthrough which the rock cuttings may be raised to the surface. By Way ofexample, such a shaft may be about forty-two inches in diameter, and theroof of the cavern (the lower end of the aforesaid shaft) may be on theorder of several hundred feet below the surface. To keep this main shaftopen, a casing, of fortytWo inches I.D. for example, is cementedtherein, in much the same way as the casing is cemented in an oil well.This casing is left in the shaft when the cavern is completed, and isused for various purposes (e.g., cavern inspection or maintenance)during the operation of the cavern. One of the main functions of thiscasing, during cavern operation, is to provide a convenient way forconducting the cavern till pipe to the cavern; this till pipe, which mayfor example be of six inches ID., extends downwardly through the casing,from the surface of the earth to the interior of the cavern, in adirection substantially parallel to the longitudinal axis of the casing.Suitable valves, pumps, etc. are coupled to the upper end of the iillpipe, for pumping the uid (which may for example be a liquefiedhydrocarbon such as propane or butane) under pressure into the cavern,for storage.

The upper end of the casing may be approximately even with the surfaceof the earth, for example; the lower end of the casing may beapproximately even with the top or roof of the mined rock cavern.

The arrangement described, for the subterranean storage of uids atsuperatmospheric pressure, presents several possible re hazards. In thefirst place, in the event that a ssure should develop at the top of thecasing, the stored pressured fluid from the cavern would be free to gushout through this lissure, giving rise to an extremely dangeroussituation from the standpoint of fire, if hydrocarbons are being stored.Additionally, in case the fill line or pipe above the surface of theearth should break, the hydrocarbon stored in the cavern could rush outthrough this break, resulting in a great tire hazard.

An object of this invention is to provide an improved arrangement forthe underground storage of fluids such as hydrocarbons.

Another object is to provide an arrangement for materially reducing there hazard in connection with the subterranean (underground) storage ofhydrocarbons such as propane.

A further object is to provide an arrangement, for underground storagecaverns, which will positively prevent the stored fluid from leaving thecavern in the event that a crack or break should occur at the top of thecasing.

A still further object is to provide an arrangement, for undergroundstorage caverns, which will prevent the stored iluid from leaving thecavern in the event that 2 a break occurs in the fluid ll line, abovethe surface of the earth.

The objects of this invention are accomplished, briey, in the followingmanner. In the preferred ernbodiment, a substantially cylindricalpressure vessel, on the order of twenty feet in length, is welded inlengthwise position onto the top of the casing utilized with the cavern,the arrangement being such that the lower dished head or closure of thisvessel is located about ten feet below the surface of the earth, orgrade This lower closure seals oi the cavern at a point below grade. Thecavern iill pipe or line passes down through this pressure vessel andthrough the casing; this line extends downwardly into a sump provided inthe floor of the cavern, beneath the casing. In the sump there is aquantity of a sealing liquid, which would normally be water. The depthfrom grade to the sump is such that the vertical length of the till pipeis somewhat in excess of the length of a column of sealing liquidnecessary to counterbalance, by hydrostatic pressure, the effectivepressure of the stored fluid. In another embodiment, no pressure vessel(and, therefore, no lower dished head) is used with the casing, 4butinstead the large-diameter casing is swaged down to a smaller diameterat a level about even with the cavern roof, and this smallerdiameterportion extends down into the aforementioned sump. In this embodiment,the fill pipe passes down through the casing into the sump, as before.

A detailed description of the invention follows, taken in conjunctionwith the accompanying drawings, wherein:

FIGURE l is a schematic or overall representation of a generallypreferred subterranean cavern arrangement according to this invention;

FIGURE 2 is a longitudinal section through the FIG- URE 1 arrangement,drawn on an enlarged scale to show details; and

FIGURE 3 is a view somewhat similar to FIGURE 2, but showing a modiedarrangement.

Referring rst to FIGURE 1, which is a somewhat schematic representationof a completed cavern arrangement, a subterranean mined cavern 1 canserve as a storage container for a uid 2 under pressure. For purposes ofillustration, the cavern will Ibe described as being utilized for thestorage under pressure of propane, in a liquid state. However, it ispointed out that it can be used for the storage of other highly volatileliqueiied hydrocarbons, such as butane, or `the material known ascasinghead gasoline. Also, it can be used for the storage of variousother iluids (either liquids or gases), whether or not they arehydrocarbons. The uid 2 (propane, for example) is stored undersuperatmospheric pressure in the cavern l, to allow storage of thismaterial in its liquid state. Propane may be stored in such a cavern,for example, at a pressure on the order of pounds per square inch,absolute. At this pressure, propane has a boiling point of about 84 =F.,which means that it does not boil at the temperatures ordinarilyencountered in subterranean caverns.

In order to mine the cavern 1, a large-diameter main or working shaft 3(having a diameter on the order of forty-two inches or more) is utilizedfor the purpose of moving men, materials, equipment, rock cuttings, etc.between the surface of the eanth (denoted by grade level 4) and thecavern 1 proper. Shaft 3 is several hundred feet in length, and in atypical example may be about 380 feet long. In other words, the distancefrom grade 4 to the roof of cavern 1 may be about 380 feet. Prior toexcavation or mining of the cavern proper, the casing 5 (of forty-twoinches LD., for example) is run into the shaft 3 and is cementedtherein, as indicated at 6. The technique here is quite similar -to thatused for cementing casing strings in oil wells. Thus, the lower end ofthe casing 5 is located, in FIGURE. 1, substantially even with the topor roof of the cavern 1, and this casing is on the order of 380 feetlong. rl`he cavern itself may be about forty feet high, from iloor toroof. All of the construction so far described is quite conventional.

Now referring to FIGURE 2, the bottom or base cylindrical shell or skirt7 of a pressure vessel 8 is buttwelded onto the top of casing 5, at apoint about thirteen feet below grade 4. This pressure vessel 8 is aprefabricated vessel which has been suitably stress-relieved, andincludes a bottom dished head or closure 9, and an upper removable heador closure 10. The main portion of vessel y8 is cylindrical with an LD.of forty-two inches, tapering down to an LD. of twenty-three inches atthe top, adjacent closure ltl. It may be seen, in FIGURE 2, that thebottom closure 9 is permanently sealed to vessel 8 adjacent the skirt 7;also, the vessel 8 is welded in lengthwise position onto the top of thecasing 5. The closure 9 is located a distance of ten feet, more or less,below grade 4, and provides a closure which in eiect seals off thecasing 5 (and the cavern 1) from the interior 'of pressure vessel 8 andalso, of course, from the atmosphere above the surface `4.

The cylindrical outer wall of a manway 11 (having a diameter of sixteeninches, for example) is sealed through the bottom closure 9; the bottomend of this manway opens into the interior of the casing 5 and the topend of this manway is sealed oit by means of a removable manhead 12. Themanhead 12 is provided with a Ivent and gate valve (for example, 11/2inches in diameter), which may be opened when desired, for ventingpurposes. Upon removal of the upper closure and the manhead 12, accessmay be had, via the manway 11, for inspection and/or maintenance of thecavern. Of course, Iduring use of thecavern 1 for storage of a fluidproduct 2, the manhead 12 and the upper closure 10 are in sealedposition, and the valve 13 is closed.

As previously stated, the bottom closure 9 is sealed to vessel 8; theupper closure 10 is also normally sealed to vessel 8. Therefore, the1interior of vessel 8 constitutes a sealed enclosure, sealed off fromboth the cavern 1 (and casing 5) and the atmosphere. The interior ofvessel 8 is pressurized to a small positive (superatmospheric) pressure(on the order of titty pounds per square inch absolute, for example)with inert gas. This may bevdone through a small (one inch diameter)pipe 14 which extends through the upper closure 10 and which tisprovided with a rvalve 15 on its outer end. The valve 15 may also beused for venting, vwhen access to the cavern is desired. Of course, thevalve 15 is closed during use of the cavern for storage purposes. Apressure gauge 16 is coupled to pipe 14, between valve y15 and closure10, for indicating the pressure in vessel 8. This inert gas tilling isused for several reasons. In the iirst place, it is desirable to have anon-ammable (and of course non-explosive) material at the surface of theearth, above the cavern. In the next place, the use of a small positivepressure of gas here (this Vpressure being less than that underWhich'the liquid 2 is stored in the cavern), lin tconjunction withpressure gauge 16, will provide an indication of leaks. If the pressure,as measured by gauge 16, increases or goes up, it means that thematerial in the cavern is leaking into the pressure vessel 8. If thispressure decreases or goes down, it means that the vessel 3 itself isleaking.

The upper end of the vessel S projects above the grade or ground level4. For example, the vertical distance between grade 4 and the upperwelded seam 17 of the cylindrical portion of vessel 8 may be about threefeet. The lower portion of vessel 8, from the lower end of skirt 7 to apoint slightly above ground level `4, is cemented into the earth. Theentire upper portion of this vessel, including the upper closure 10 iscovered or lagged with an outer coating of heat-insulating material 18,and over the top of this there is a sheet metal jacket 19. As previouslystated, the upper closure 10' is sealed (by any suitable well-knownfastening means, not shown) to vessel 8, but is capable of being removedtherefrom when desired.

ln prior constructions, a portion of the casing necessarily projected orextended above the ground level, to accommodate various pipes andvalves. With such constructions, if a iissure should happen to developat the top of the Casing, above the ground level, propane from thecavern (stored under superatmospheric pressure therein) would gushthrough this iissure, creating a very dangerous situation from thestandpoint of re. in contrast, the arrangement of the present inventionentirely eliminates this possibility. It may be seen that the presentconstruction employs a sealed closure 9 below ground level. Thus, evenif a iissure should develop above ground level 4 anywhere in vessel 3(including the upper closure 10), the bottom closure 9 seals off thecavern 1 from the iissure, so that no propane (or other liqueedhydrocarbon being stored) can escape through such fissure. The onlything that could escape under .these conditions would be the inert gascontained in vessel 8, and this is of course harmless.

A iill line or till pipe 2@ (LD. of six inches, for example), having asuitable valve 21 on its outer or upper end, is sealed through thecylindrical wall of pressure vessel 8, above the ground level 4, andpasses downwardly through this vessel. This till pipe is sealed throughthe bottom closure 9 and extends down into a sump 22 provided in the oorof cavern 1, beneath the lower end of casing 5. The lower end of pipe2i) is spaced slightly above the bottom of the sump. Sump 22 may beabout twenty feet deep below the floor of cavern 1, and the volume ofthis sump is approximately 1.5 times the internal volume of the fillpipe 20, from the lower end thereof up to valve 2x1 above the groundlevel 4.

Sump 22 permanently contains a suitable sealing liquid 23, which isnormally water. The characteristics which the sealing liquid 2.3` musthave are: a specific gravity greater than that of the stored tluid,insolubility in this fluid, and immiscibility with this fluid. Water hasthese characteristics when the fluid is a hydrocarbon such as propane,and is desirable because it is inexpensive. The use of water as thesealing liquid in the sump would be appropriate for any cavern in whichwater does not affect the environmental rock structure, such as Cavernsmined out of granite or sandstone. However, for caverns which are minedout of shale beds, it would be necessary to use a non-aqueoushydrocarbon-insoluble liquid instead of water, since the latter wouldcause shale to turn into mud. Glycerine and mercury are examples ofsuitable non-aqueous hydrocarbon-insoluble liquids which could be usedin such an environment.

When it is desired to add fluid to the cavern 1, valve 21 is opened, andthe iluid is pumped, under superatmosphenic pressure, through till pipeZtl into the sump 22, from whence it ilows through the water, or othersealing liquid 23 in the sump, upwardly into the cavern 1.

The Huid stored under pressure in the cavern 1 is removed or abstractedtherefrom, as desired `for use, in any suitable manner known in the art.For example, two deep-well pumps may be utilized, each pump beingpositioned in a respective sump (not shown) extending downwardly fromthe Hoor of the cavern. rl.`hese pump sumps are spaced sideways orlaterally from the main shaft 3. Each pump is driven by a rotating shaftfrom a respective source of power (e.g., a motor) at the surface. Thepumps are suspended within respective outer casings by respectivedischarge tubings. The pump intakes are located in the respective pumpsumps, and the pumps pump fluid from these sumps Ithrough the respectivedischarge tubings to the surface. For a more complete disclosure of sucha cavern discharge arrangement, reference may be had to the copendingapplication Serial No. 44,158, tiled July 20, 1960. If two pump sumpsare utilized, two small water pipes (three inches in diameter, forexample; not shown herein) may be sealed through the cylindrical wall ofvessel 8, these pipes passing downwardly through this vessel and throughbottom closure 9 and proceeding down to the door of the cavern, fromwhence they fan out to the respective sumps wherein are located theaforementioned discharge pumps. These last-mentioned water pipes providea safety feature, in case the pump casings should break or crack aboveground. lf this occurs, water can be rapidly pumped (by a low-pressurepump) through the appropriate pipe down into the proper sump and up intothe pump casing until the hydrostatic pressure in the sump and casingexceeds the vapor pressure of the hydrocarbon product in storage in thecavern, creating a water seal. Once the seal is created (and this can beeffected quite rapidly), the stored hydrocarbon cannot escape, it beingretained in the cavern. Substantial fire hazard, and substantial loss ofvaluable product, are thus prevented. These water pipes also function toenable repair and inspection of the deep-well pumps, as described in theaforementioned copending application. If only a conventional till pipe(without the sump and the sealing liquid) were used with the cavern, incase the 4iill pipe should break or crack above ground, or if the valve21 should leak, the fluid (e.g., hydrocarbon) stored in the cavern wouldrush out (since it is stored under superatmospheric pressure) throughthe break, creating a great fire hazard. However, the arrangement ofthis invention eliminates entirely this possibility. If the fill pipe 20should break above ground 4, or even if the valve 21 should leak thewater (or other sealing liquid 23) maintained permanently in the sump 22would rise in the till line 20 (under the influence of the pressuredfluid (hydrocarbon)) in the cavern until it reached a level or height atwhich its hydrostatic head (plus, of course, atmospheric pressureexerted on the upper face of this sealing liquid, since lthe upper endof pipe 26 would then be open to the atmosphere, by way of theaforementioned break) would counterbalance the pressure of thehydrocarbon 2. Since this last-mentioned level at which the aforesaidbalance occurs is considerably below ground level 4 (as will later beexplained), by way of a numerical example), no hydrocarbon can escapefrom the cavern by way of the broken or cracked fill pipe. The pressureof the stored hydrocarbon is insuflicient to overcome the hydrostaticpressure exerted on it, and it is therefore retained in the cavern.Thus, there is no iire hazard, and no loss of valuable product.

Assuming a pressure in the cavern of 150 pounds per square inch absolute(equivalent to 135.3 pounds per square inch gauge), and assuming wateris the sealing liquid, a hydrostatic head of about or about 295 feet,would be needed to balance the pressure of the hydrocarbon in thecavern. This height of water is considerably less than the 38() feet ormore (actually, about 440 feet) or length (below ground level 4)provided in pipe Ztl. Of course, if higher-specificgravity liquids suchas glycerine or mercury were utilized as the sealing liquid, thehydrostatic head required for balance would be even less than about 295feet.

A small-diameter pipe or line 24 (one inch in diameter, for example)having a valve 25 on its outer or upper end, is seded through thecylindrical wall o-f pressure vessel 8, above the ground level 4, andpasses downwardly through this vessel. Pipe 24 is sealed through thebottom closure 9 and extends down into the sump 22 but terminates at aknown, predetermined level which is above the bottom end of fill pipe20. This predetermined level of lthe lower end of line 24 (relative tothe bottom of sump 22, vfor example) is so adjusted that when the levelof sealing liquid in sump 22 is at least as high as the lower end ofthis line, there will be sufficient sealing liquid in the sump toperform the abovedescribed function of balancing the pressure of thehydrocarbon (by means of hydrostatic head), in case the cavern till linebreaks. Therefore, the small line 24 can be used as a gauge line, fordetermining whether or not sufficient sealing liquid 232 is present inthe sump 22. During normal cavern operation, of course, valve 25 wouldbe closed. However, when it is desired to ascertain whether suicientliquid is present in the sump, valve 25 is opened. Let us assume thatthe cavern contains liquefied hydrocarbon as illustrated in thedrawings. If the hydrocarbon product issues from the valve 25 when thelatter is opened, it means that the level of sealing liquid is below thelower end of line 214 (such lower end then contacting the hydrocarbon);there is then insuicient sealing liquid in the sump. If no liquid issuesfrom valve 25 when the sarne is opened, it means that there issufficient sealing liquid in the sump. In this latter case, the actionis similar to that occurring when a break develops in the till line;water then raises in the gauge line 24 until it reaches a level at whichits hydrostatic head balances the pressure of the hydrocarbon, and sincethis latter level is below the ground level 4, nothing (except possiblygas or vapor) emerges from line 24.

A small-diameter pipe or line 26 (three inches in diameter, forexample), having a valve 27 on its outer or upper end, is sealed throughthe cylindrical wall of pressure vessel 8, above ground 4, and passesdownwardly through this vessel. Pipe 26 is sealed through the bottomclosure 9 and extends down into the cavern 1, terminating about sixinches beneath the roof thereof. A pressure gauge 28 is coupled to line26, between valve 27' and vessel 8, for indicating the pressure in thecavern. Line 26, in addition to its pressure-indicating function, servesas a vent line (when the cavern is being filled), and also as a gaugetube, to indicate the maximum filling point of the cavern (whenhydrocarbon begins to issue from line 26, valve 27 then being open, itis known that the cavern is full). In addition, line 26 may be used inconjunction with line 24 to determine the liquid level in the cavern.

The pressure equalizing line 26 has, of necessity, no safety featuresuch as that associated with the lill pipe 26. However, even if afissure should develop above ground level in vessel 8, it is unlikelythat pipe 26 would also break. On the other hand, if it is expected thatpipe 26 might break, certain well-known design expedients could beresorted to, for reducing the possibility of breakage. One of thesemight be to run pipe 26 out of thevessel 8 below ground level, to encaseit in concrete, and to carry it underground for several feet before itconnects with other surface piping.

Although not shown in the drawings, it is desirable that all of the pipeconnections to the cavern be provided with check valves.

Although not strictly necessary for sealing purposes, it is desirableIthat an upper closure 10 be utilized, to keep rain, debris, etc. out ofthe space above bottom closure 9; also, of course, the upper closureprevents personnel from falling down into this space. Actually, theutilization of the upper closure .10 (or of a complete pressure vessel8, `as described) allows for an inert gas filling above the cavern andcasing, which is desirable. AlsoV (and this should be obvious), the useof two separate closures 9 and 10 gives double the protection againstleaks.

v2, but illustrating a modified construction.

.In this modified construction, no pressure vessel is secured to thecasing, and therefore no bottom closure is employed, and no inert gasiilling is utilized. Instead,

fthe hydrostatic head of a sealing liquid is used 4to counterbalance theeffective pressure `of the stored hydrocarbon,

when a crack occurs at the top of the casing, above vground level. Thismodified embodiment will now be described in more detail.

In FIGURE 3, the casing (forty-two inches 1.1).) is cemented inthe mainshaft like casing 5, butl casing 5 is extended up above rground level 4,and is sealed off with `an upper closure in which there -is sealed amanway or manh-ead 29 with a sealed but removable cover. A vent pipe 14is sealed through the casing cover and is provided with a valve 15, forenabling venting before access to the cavern is effected. In this case,the pressure gauge 16 is not strictly necessary, thou-gh it may beemployed if desired.

The casing 5 is --swaged down to a smaller diameter l (twenty inchesLD., for example) at a level approximately even with the bottom end ofthe main shaft. From this point, the smaller-diameter portion 3l) of thecasing extends downwardly into sump 22 (provided,

like sump 22, in the floor of the cavern, below the lower end of themain shaft), terminating near the bottom of the sump. The sump 22 mustbe considerably larger than the sump 22, since the former must contain4enough sealing liquid to provide a hydrostatic-head type seal in thelarge-diameter casing 5', as Well as in the reduced-diameter Iportion ofthe casing.

In the FIGURE 3 arrangement, if a crack or fissure occurred at the topof casing 5 anywhere above ground level 4 (thus opening the upper end ofcasing 5' to the atmosphere), the sealing liquid 23 would be forced upthe smaller-diameter portion 30 of the casing (and on up into thelarger-diameter portion thereof, as well), rising to a level or heightat which its hydrostatic head (plus the atmospheric pressure)would'counterbalance the pressure of the hydrocarbon 2. Thislast-mentioned level is considerably below ground level 4. Therefore, nohydrocarbon can escape from the cavern by way of .the casing crack orssure.

4In FIGURE l3, the fill line or fill pipe 20 is sealed through the sidewall of casing 5', vand extends down through this casing and through thereduced-diameter .casing por-tion B10-into sump 22', terminating nearthe bottom of the sump, as in FIGURE 2. In the event of a crack or breakin the ll line 20 above ground, the :sealing liquid -23 rises in thisline in the same manner .as in FIGURE y2, until thehydrostatic headcounter- .balances the pressure of the hydrocarbon 2. Again, Vnohydrocarbon can escape from the cavern 1 by way -of the broken orcrackediill line.

In FIGURE 3, the ygauge line. 24' is sealed through the side wall ofcasing 5', and extends down through this casing and through thereduced-diameter casing portion 30 to the lower end of this casingportion, at which point line 24 makes a reentrant turn to proceedupwardly to its termination in sump 22 at a known, predetermined levelabove the Ibottom end of ill pipe 20. Line 24 is used asis line 24 inFIGURE 2, fOr determin- S ing whether or not sufficient sealing liquid23 is present in the sump 22'. In FIGURE 3, it must be determined (bymeans of this gauge line) whether or not sullicient sealing liquid ispresen-t for the 'two types of hydrostatichead seals involved in FIGURE3.

In the modiiied construction, the vent and gauge line 26 is sealedthrough the side wall of casing 5 and extends down through this casingand through the reduceddiameter casing portion 30 to the lower end ofthis casing port-ion, at which point line 26 makes a reentrant turn toproceed upwardly to its termination, about six inches beneath the roofof the cavern 1. Line 26 serves the same purposes, and operates in thesame way, as doesl line 26 in FIGURE 2. t A -manhead or manway 31 issealed into the transitio section between the large-diameter casing 5and the smaller-diameter casing portion 30, this manway having a sealedbut removable cover. Preferably, a vent and gate valve`r(not shown) areprovided in the latter cover, simliar to the valve 13 in FIGURE 2. Uponremoval of the covers on manways 29 and 31, access may be had, via thesetwo manways, for inspection and/or maintenance of the cavern. Of course,during use of the cavern 1 for storage, the covers on these manwayswould be closed and sealed.

The invention claimed is:

l. In a subterranean cavern for storing a fluid at superatmosphericpressure, said cavern having a communicating shaft extending from thesurface of the earth downwardly to the cavern: a casing sealed in saidshaft, a closure sealed into said casing at a point below the surface ofthe earth, a sump extending downwardly from the door of said cavern, aquantity of a sealing liquid maintained permanently in said sump, saidsealing liquid being irnmiscible with a uid stored in said cavern andhaving a higher specific gravity than such stored fluid; a till pipe forsaid stored fluid sealed into said casing, extending downwardly therein,sealed through said closure, and extending through said stored fluid andopening into solely the sealing liquid in said sump; and another closuresealed to the upper end of said casing, above the surface of the earth.

2. `In a subterranean cavern for storing a liquid at superatmosphericpresure, means providing a seal between a liquid hydrocarbon stored insaid cavern and the atomsphere, a sump extending downardly from thefloor of said cavern, a quantity of water maintained permanenti ly insaid sump, and a cavern fill pipe through which only the stored liquidhydrocarbon ofws into said cavern, said pipe extending from the surfaceof the earth vertically downwardly through said seal and through saidstored liquid hydrocarbon, and opening into solely the water in saidsump, the volume of said sump being at least 1.5 times the internalvolume of said fill pipe, from the lower end thereof to the surface ofthe earth, and the vertical length of said ll pipe being in excess ofthe length of the column of water necessary to counterbalance, byhydrostatic pressure, the effective presure of the stored liquidhydrocarbon.

References Cited in the le of this patent UNITED STATES PATENTS'2,337,472 Kares Dec. 21, 1943 2,459,227 Kerr Jan. 18, 1949 2,659,209Phelps Nov. 17, 1953 2,745,647 Gilmore May 15, 1956 2,749,714 HunterJune 12, 1956 2,880,593 Johnson Apr. 7, 1959 2,884,761 Miles May 5, 19592,942,424 Koble June 28, 1960 2,971,344 Meade Feb. 1 4, 1961

1. IN A SUBTERRANEAN CAVERN FOR STORING A FLUID AT SUPERATMOSPHERICPRESSURE, SAID CAVERN HAVING A COMMUNICATING SHAFT EXTENDING FROM THESURFACE OF THE EARTH DOWNWARDLY TO THE CAVERN: A CASING SEALED IN SAIDSHAFT, A CLOSURE SEALED INTO SAID CASING AT A POINT BELOW THE SURFACE OFTHE EARTH, A SUMP EXTENDING DOWNWARDLY FROM THE FLOOR OF SAID CAVERN, AQUANTITY OF A SEALING LIQUID MAINTAINED PERMANENTLY IN SAID SUMP, SAIDSEALING LIQUID BEING IMMISCIBLE WITH A FLUID STORED IN SAID CAVERN ANDHAVING A HIGHER SPECIFIC GRAVITY THAN SUCH STORED FLUID; A FILL PIPE FORSAID STORED FLUID SEALED INTO SAID CASING, EXTENDING DOWNWARDLY THEREIN,SEALED THROUGH SAID CLOSURE, AND EXTENDING THROUGH SAID STORED FLUID ANDOPENING INTO SOLELY THE SEALING LIQUID IN SAID SUMP; AND ANOTHER CLOSURESEALED TO THE UPPER END OF SAID CASING, ABOVE THE SURFACE OF THE EARTH.